This Instructable will show you how to create your own garage laser parking system (the modern day version of the tennis ball on a string.) Stop now if you don't have a basic understanding of electronics or how to safely use a multimeter. I take no responsibility for any damage done to you, others, your property, or the property of others!
- Garage door opener with a light that automatically turns on when the door opens
- Cheap laser pointer
- Voltmeter / multimeter
- Soldering iron & solder
- Needle nose pliers
- Wire cutters and strippers
- Rotary tool (Dremel, etc.)
- Small zip ties
- Sacrificial AC adapter (wall wart)
- Heat shrink tubing
- Light bulb socket outlet adapter
- "Short" light bulbs
One small side note here: LASER is actually an acronym, standing for "Light Amplification by Stimulated Emission of Radiation." I will not be spelling it using all caps in this Instructable, however.
Step 1: Determining the Operating Voltage and Polarity
The first step is to determine the polarity of the battery contacts and the voltage needed for your laser pointer to operate.
Remove the laser's battery cover - usually just a screw-on back. Before removing the button cell batteries, take a look at how they are oriented. Button cell batteries typically have their positive terminal on the flat side with all of the writing, leaving the other side with the negative terminal. The writing on the flat side should have a plus or a minus indicating this. If the flat (positive) side is facing the rear of the laser, that means the chassis acts at the positive contact. There should be a spring or something similar acting as the negative contact on the back of the laser's circuit board underneath the batteries.
Take the button cell batteries out, count them, and multiply that number times 1.5 (button cell batteries are typically 1.5V each.) The resulting number is the total voltage needed for your laser to work. For example, if your laser pointer uses two button cell batteries, it will require ~3V to operate.
Step 2: Choosing the Correct AC Adapter
Once you know the laser pointer's operating voltage, find an AC adapter that outputs near the same voltage. You'll be okay if its output is 1-2V higher than what your laser pointer requires, but don't go much higher than that or you'll risk damaging the laser and/or start a fire. I ended up using one from Radio Shack that's adjustable from 1V up to 12V.
Example: A 3V laser pointer can usually operate on a 4-5V AC adapter (your mileage may vary.) Be careful and try to get as close to the actual operating voltage as possible.
Step 3: Preparing the AC Adapter
NOTE: Be very careful! Even though you're dealing with relatively low voltages on your AC adapter, it's the current that will kill you!
When you've selected the right AC adapter, cut the end off, separate the two wires, strip the ends, and hold them apart using some kind of insulator (wood, etc.) Once the two wires are separated and aren't touching anything conductive, plug the AC adapter in and use your multimeter to determine which wire is positive and which is negative. Again, do not attempt this if you don't know how to safely use a multimeter!
Step 4: Preparing the Laser
The next step is to remove the laser from its housing. Typically everything will be soldered to one small circuit board and it should all come out in one piece. I won't go into much detail here since this can vary depending on the type of laser pointer that you've decided to use. The one I chose had to be cut out of its metal housing with a rotary tool. Do what you need to do here, but be careful not to damage it!
Step 5: Connecting the AC Adapter
Now that you have your laser's guts exposed, you can take a closer look at the circuit board. Remember when I told you to look at the orientation of the battery poles? Now's when you'll need that info. For this tutorial, I'll assume that the positive battery terminal was contacting the laser's metal chassis, and the negative battery terminal was in contact with the laser's circuit board. Adjust as needed for your laser.
My laser had a metal spring soldered to the rear of the circuit board that was acting as the negative battery terminal. I simply removed this by heating up the solder and pulling the spring away with a pair of needle nose pliers.
Make sure to slip any heat shrink tubing that you're going to use over the AC adapter's wires before soldering them to the laser! This will save you some frustration later!
When everything is ready, just solder the two wires from your AC adapter into place. I soldered the negative wire to the rear of the circuit board where the spring had been attached, and the positive wire to the bottom of the circuit board where the brass laser output housing is attached.
After connecting your wires, plug in the AC adapter and attempt to operate the laser using the button, switch, etc. If it works, great! If not, you'll need to go back and find out what went wrong. Some possible causes include:
- Incorrect AC adapter output voltage (too low or too high.)
- Wires from the AC adapter are connected in reverse.
- Solder joints aren't making a good connection.
- Positive and negative circuit board terminals not correctly identified/used.
Step 6: ...aaand Doctor
Slide the heat shrink tubing into place and apply some heat with a lighter, match, etc. until it shrinks down. Don't heat it for too long or you'll cause it to burn and/or melt. I used two different sizes: a smaller piece (1/4") to cover the negative connection, and a larger piece (1/2") to cover the laser's circuit board.
To make sure that the laser comes on whenever power is applied via the AC adapter, I used a small zip tie to hold the power button down. Sure, you could solder a short across the button so that it's always on, but this is how I did it. Do whatever works best for you and the type of laser you have.
Finally, open up your garage door opener to expose the light bulb and remove it. Screw in the light bulb socket outlet adapter, screw in a light bulb (I had to use a shorter one to fit), then plug your laser into the new outlet. Test to make sure that the laser turns on and off with the bulb as the garage door operates. If everything checks out, simply mount it on your garage's ceiling and point it at a spot on your vehicle's dashboard so that you know when to stop!